ITAR-TASS said the blast was near metal detectors stationed at the entrance to the city's main train station.

Volgograd - known as Stalingrad in the Soviet era - was attacked in October by a female suicide bomber with links to Islamists fighting federal forces in Russia's volatile North Caucasus.

The October 21 strike killed six people aboard a crowded bus and raised security fears ahead of the Winter Games in Sochi, to run from February 4 to February 23.

Sochi lies 690 kilometres southwest of Volgograd and in direct proximity of the violence ravaging North Caucasus regions such as Dagestan and Chechnya on a daily basis.

Militants are seeking to impose an Islamist state throughout Russia's North Caucasus. Their leader, Doku Umarov, has ordered his foot soldiers to target civilians outside the region and disrupt the Olympic Games.

Female suicide bombers are often referred to in Russia as "black widows'' - women who seek to avenge the deaths of their family members in North Caucasus fighting by targeting Russian civilians.

Female suicide bombers set off blasts at two Moscow metro stations in March 2010 that killed more than 35 people.

So-called black widows were also responsible for taking down two passenger jets that took off from a Moscow airport within minutes of each other in 2004, killing about 90 people.

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